Etching method

ABSTRACT

The method deals with plasma-structuring by etching, in particular with the plasma-structuring of materials at high temperatures. The application of a chemical etching process at high temperatures is made possible by the prior deposition of a polyimide mask.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

[0001] The invention lies in the materials processing field and relates, more specifically, to a method for plasma-structuring by etching, particularly for the plasma-structuring of materials at high temperatures.

[0002] Platinum, which is utilized as the electrode material in ferroelectric storage capacitors for producing non-volatile data memories (Fe-RAM), belongs to the class of materials which are advantageously structured at high temperatures.

[0003] Methods are also known for plasma-structuring using physical etching processes at relatively low temperatures (less than or equal to 100° C.), whereby the electrode (v) is primarily etched and structured by physical sputter erosion. When pure noble gases are used, a subsequent cleaning step is required owing to the formation of redepositions on the sidewall of the mask, which raises the cost of the process. When primarily reactive gases are used, intermediate redepositions also form but are removed in the course of the etching process. Since these redepositions are very voluminous, they lead to a large expansion in the etch dimensions. In addition, the physical sputter erosion and the use of reactive gases are responsible for intensive faceting of the mask and a low mask selectivity.

[0004] The use of a hard oxide mask for etching at high or elevated temperatures has also been considered. However, owing to the identical substrate material (typically oxide), topographies form when the mask is removed subsequent to etching. It is also known to utilize a metallic mask for etching at elevated temperatures. However, the disadvantage of this is that at elevated temperatures the metal diffuses from the mask into the electrode, impairing its high conductivity.

[0005] When photosensitive masks are used, the etching process is confined to low temperatures (see Nishikawa et al., Platinum Etching and Plasma Characteristics in RF Magnetron and Electron Cyclotron Resonance Plasmas, Jpn. J. Appl. Phys., Vol. 32 (1993): 6102-08). On the other hand, a plasma-etching method for etching titanates is taught in U.S. Pat. No. 5,653,851.

SUMMARY OF THE INVENTION

[0006] The object of the present invention is to provide an etching process which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and which provides for a mask that allows chemical plasma etching at high temperatures.

[0007] With the above and other objects in view there is provided, in accordance with the invention, an improved plasma-etching process at temperatures above 100° C. The novel method provides for the application of a polyimide mask prior to the etching of the structure.

[0008] The subject matter of the invention is a method for plasma-etching at temperatures above b 100° C. wherein a polyimide mask is applied prior to the etching of the structure.

[0009] The polyimide mask on the electrode makes it possible to etch at temperatures of up to 500° C. at that location. Consequently, chemical etching of the electrodes is possible, because volatile noble metal compounds, which do not arise at lower temperatures, can form with the etching gasses. A chemical etching of noble metal electrodes is superior to physical etching with respect to selectivity, etch rate, edge angle, avoidance of topographies, and so on.

[0010] Polyimides have been used hitherto as “low-∈ dielectric” (Japanese patent application JP 05-072736 A), as the material for deposit formation in galvanic deposition processes (A. B. Frazier, “Development of Micromachined Devices Using Polyimide-Based Processes”, Sensors and Actuators A 45 (1994): 47-55) and as a shadow mask (European patent application EP 0 230 615).

[0011] The polyimide mask can be easily removed after structuring by incineration.

[0012] In accordance with an added feature of the invention, the polyimide mask is made of a polyimide containing fluorine.

[0013] In accordance with another feature of the invention, the polyimide is formed on the wafer by cross-linking.

[0014] There is also provide, in an advantageous mode of the invention, a method for the plasma-etching of metals, which comprises applying a polyimide mask to a metal layer, and chemically etching the metal layer, aided by the mask, with a plasma etching process at an elevated temperature.

[0015] Preferably, the metal layer consists of a noble metal.

[0016] In accordance with an additional feature of the invention, the etching process is carried out at temperatures between 150° C. and 600° C., and preferably between 200° C. and 550° C. A specifically advantageous temperature range is between 300° C. and 500° C.

[0017] The invention makes it possible for the first time to carry out a chemical etching at elevated temperatures. The application is made possible by the prior deposition of a polyimide mask. 

We claim:
 1. An improved plasma-etching process at temperatures above 100° C., which comprises applying a polyimide mask prior to etching a structure.
 2. The method according to claim 1 , wherein the polyimide contains fluorine.
 3. The method according to claim 1 , which comprises forming the polyimide on a wafer by cross-linking.
 4. A method for the plasma-etching of metals, which comprises applying a polyimide mask to a metal layer, and chemically etching the metal layer, aided by the mask, with a plasma etching process at temperatures between 300° C. and 500° C.
 5. The method according to claim 4 , wherein the metal layer consists of a noble metal.
 6. The method according to claim 4 , wherein the polyimide contains fluorine.
 7. The method according to claim 4 , which comprises forming the polyimide on a wafer by cross-linking. 